An oxide semiconductor film comprising a metal complex oxide has a high degree of mobility and visible light transmission, and is used as a switching device, a driving circuit device or the like of a liquid crystal display, a thin film electroluminescence display, an electrophoresis display, a moving particle display or the like.
Examples of an oxide semiconductor film comprising a metal complex oxide include an oxide semiconductor film comprising an oxide of In, Ga and Zn (IGZO). An oxide semiconductor film obtained by using an IGZO sputtering target has an advantage that it has a higher mobility than that of an amorphous silicon film, and hence has been attracting attention (see Patent Documents 1 to 10).
An IGZO target is known to be composed mainly of a compound shown by InGaO3(ZnO)m (wherein m is an integer of 1 to 20). However, if sputtering (DC sputtering, for example) is conducted by using an IGZO sputtering target, a problem arises that the compound shown by InGaO3(ZnO)m grows abnormally to cause abnormal discharge, leading to the formation of a defective film.
Furthermore, an IGZO sputtering target is produced by mixing raw material powder to form a mixture, prefiring, pulverizing, granulating and molding the mixture to form a molded product, and sintering and reducing the molded product. However, due to a large number of steps, this process has a disadvantage that the productivity of a sputtering target is lowered, resulting in an increased production cost.
Therefore, it is preferable to omit even one of these steps. However, no improvement has heretofore been made on the production process, and an IGZO target is being produced by a conventional process.
In addition, the sputtering target obtained by conventional processes has a conductivity of about 90 S/cm (specific bulk resistance: 0.011 Ωcm); in other words, has a high resistance. It is difficult to obtain by conventional processes a target which does not suffer from cracking or other problems during sputtering.
Compounds, which are contained in an IGZO target and shown by InGaO3(ZnO)2, InGaO3(ZnO)3, InGaO3(ZnO)4, InGaO3(ZnO)5 and InGaO3(ZnO)7, as well as the production method thereof are disclosed in Patent Documents 11 to 15.
However, compounds shown by ZnGa2O4 and InGaZnO4 are not obtained in Patent Documents 11 to 15. As for the particle size of the raw material powder used in Patent Documents 11 to 15, these patent documents only state that a particularly preferred particle size is 10 μm or less. Furthermore, although these patent documents state that these compounds can be used in a semiconductor device, no statement is made on the specific resistance value thereof and the use thereof in a sputtering target.    Patent Document 1: JP-A-H8-295514    Patent Document 2: JP-A-H8-330103    Patent Document 3: JP-A-2000-044236    Patent Document 4: JP-A-2006-165527    Patent Document 5: JP-A-2006-165528    Patent Document 6: JP-A-2006-165529    Patent Document 7: JP-A-2006-165530    Patent Document 8: JP-A-2006-165531    Patent Document 9: JP-A-2006-165532    Patent Document 10: JP-A-2006-173580    Patent Document 11: JP-A-S63-239117    Patent Document 12: JP-A-S63-210022    Patent Document 13: JP-A-S63-210023    Patent Document 14: JP-A-S63-210024    Patent Document 15: JP-A-S63-265818